Description of the Prior Art
Railroads today almost universally employ the split switch design. The split switch is composed of a switch proper for the diversion of the wheels, a frog to carry the wheel flanges across opposing rails, lead rails between the frog and the switch proper, guardrails to prevent batter and misrouting at the frog point, and a set of switch ties to support the assemblage. The switch proper includes a set of fixed stock rails and a movable pair of switch point rails. Each switch point rail has a knife-edged free end, called a point, and a pivotally fixed end, called a heel. Depending on which way the switch is thrown, the stock rail side of the point of one or the other of the switch point rails fits snugly against the gauge side of the adjacent stock rail.
In order to protect the point from direct battering contact with the train wheels, a pocket is usually milled into the gauge side of the head or ball of the stock rail to accommodate the precise nesting abutment of the point and a lateral portion of the switch point rail of which it is a part. The most commonly used design is the Samson Switch point design as illustrated in FIG. 1. FIG. 1 shows switch rail point 12 in nesting abutment with stock rail 15 at the point of the switch. The Samson Switch point design requires that the stock rail pocket be milled into the rail head 18 position starting 0.5 inches vertically down from the horizontal plane containing rail head top surface apex 19, that is at distance H, and at an angle .theta. of 18 degrees 25 minutes with the pocket extending 9 to 24 feet in length, depending on the switch, with lead-in and lead-out taper zones each 3 inches in length.
Heretofore, in order to obtain the required precision repeatably and efficiently, the stock rail pocket had to be machined under shop conditions rather than in place in the field. Although such pockets can be field formed by hand-operated grinders, such grinders are difficult to control, subject the rail to localized overheating, require a long time to form the pocket, and the results greatly depend on the skill and patience of the operator. The necessity of shop milling produces the significant and costly disadvantage that where the track line consists of continuous welded rail (CWR), the up to quarter mile long sections of ribbon rail that otherwise comprise the CWR rail line cannot be used as the rail through either the curved side or the straight side of a switch. Instead, the rail through each side of a switch must be made up of several short sections of rail in order that one of them can have the necessary pocket milled into it under machine shop conditions. It is, therefore, necessary, at least on the straight side of the switch, to field weld the several short rails to each other as well as to the ribbon rail on each end of the switch. For the curved side of the switch, either welding or bolting may be used to join together the several sections of short rail depending on the nature of the switch. The disadvantage is compounded by the fact that due to the spatial confinements imposed by the hardware associated with a switch, automated field welding equipment cannot be used to make the field welds of the several switch short rail sections. Thus, it is necessary to rely on the labor-intensive and time-consuming practice of manual field welding to make these several field welds. Typically, the set-up, welding, and grinding associated with each manual field weld takes a two-man crew on the order of two hours to complete making manual welds expensive to perform.
Therefore, there is a need that has existed since the introduction of CWR in the 1930's for a simple to operate means and a simple to perform method for field machining stock rail pockets into CWR rail that are capable of producing consistently reproducible, precise milling results efficiently and cost effectively.